Fuels based on biocomponent sources will become increasingly prevalent in the future. Already, various governments have instituted current and future requirements that motor fuel pools contain a minimum percentage of fuel derived from a biocomponent source, such as a plant, animal, fish, or algae based oil or fat.
Producing diesel fuel from biocomponent sources presents a variety of challenges. For mineral oil feeds, one of the major problems has been the removal of sulfur and nitrogen heteroatom compounds, in order to comply with regulatory specifications regarding permissible levels of such heteroatoms in fuels. Extensive research has been performed on hydroprocessing methods as well as other methods for removing such heteroatoms. One advantage of some biocomponent feedstocks is that the feeds do not typically contain substantial sulfur and/or nitrogen contamination. However, this advantage is offset somewhat by the presence of other compounds in biocomponent feeds, such as oxygen-containing compounds.
U.S. Patent Application Publication No. 2008/0161614 describes two stage co-processing of a feed including both vegetable/animal and mineral oil. The first stage is operated at lower severity to primarily treat the vegetable and/or animal oil in the feed. The product of the first stage is then stripped to remove gas phase impurities. The stripped product is then hydrotreated in a more severe hydrotreatment stage to produce a diesel fuel.
U.S. Patent Application Publication No. 2007/0175795 describes a method for hydroprocessing mixtures of mineral oils, such as light cycle oils, and triglyceride containing materials, such as vegetable oils. The method can be used with a fluidized bed reactor.
U.S. Patent Application Publication No. 2008/0173570 describes a two stage hydrotreatment process. In a first stage, a deep hydrodesulfurization is performed on a mineral (gas oil) feed to meet a desired specification. At least a portion of this desulfurized mineral feed is then combined with a feed having at least a portion from a vegetable or animal source. The mixed feed is hydrotreated in a second reactor to make a gas oil fuel base.
PCT Publication No. WO/2008/020048 describes a method for hydrotreating mixtures of triglycerides and vacuum gas oil. Use of an ebullating bed for the hydrotreatment step is noted as a preferred embodiment. However, no examples of use of an ebullating bed are provided.